Earth Day is celebrated worldwide on April 22nd, a day dedicated to increasing awareness and appreciation of the Earth's natural environment, including bats. See Earth Day 2013 for local resources and ways to celebrate Earth Day.

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Eleven years ago today, the U.S. Fish and Wildlife Service approved the first Habitat Conservation Plan for Indiana bats. This plan protected a maternity colony near the Indianapolis Airport while allowing development in the area.

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The cycle of day and night is a primary driver of behavior and physiology in most mammals, and mammals have a biological “clock” that senses and responds to this cycle. But how does a bat hibernating in total darkness maintain its biological clock? Keep reading bat facts!

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During hibernation, arousal bouts in some bats are synchronized with dusk, even though the bat is in constant darkness. Something other than light must cue the bat’s internal clock, but how bats maintain these daily cycles in the absence of light is a mystery.

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Arousal frequency in hibernating Indiana bats is lowest during the coldest winter months. As air temperatures warm in April, arousals become more frequent and bats start taking flights outside hibernacula on milder evenings.

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In dark caves with almost constant air temperatures, how do bats know that spring is coming? Dwindling fat reserves may signal bats that it’s time for spring emergence.

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Bats likely can detect subtle changes in temperature and air movement in hibernacula as spring approaches. Whatever the cue, hibernating bats sense that spring is approaching. They may switch roost locations in hibernacula and hibernating bats may cluster more loosely.

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The date that Indiana bats emerge from their hibernacula in spring varies across the species’ range. In warmer parts of the range and in years with an early spring, bats emerge from hibernation earlier. Rangewide, spring emergence generally peaks in April.

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In the 1960s, researchers trapped bats at cave entrances in Indiana and Kentucky to study spring emergence. Mid-April was the peak time for departure of female bats, even though most males were still hibernating.

Indiana bats mate in the fall. Females store the sperm throughout winter and become pregnant after spring emergence from hibernation when fertilization actually occurs.

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Delaying pregnancy until spring is an advantage for Indiana bats. As bats emerge from hibernation their metabolism speeds back up, they again become euthermic, maintaining a high body temperature, and insects become available. All of these changes help support pregnancy and embryo development.

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Spring emergence is a stressful time for bats. Fat reserves are at the lowest point of the year and insect availability can be spotty. It is particularly stressful for females that have high energy demands from pregnancy and must migrate to their summer maternity habitat.

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Indiana bats do not necessarily stay in the same spot during hibernation. During arousals they have to maintain a higher body temperature, so to save energy they may move to warmer locations within the cave.

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Tomorrow is National Poem in Your Pocket Day. The idea is simple, select a poem you love and carry it with you to share with co-workers, family, and friends. Why not find a poem about bats?

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In case you didn’t find a bat poem, here’s one for your pocket to celebrate National Poem in Your Pocket Day:

Batty by Shel Silverstein

The baby bat
Screamed out in fright,
“Turn on the dark,
I'm afraid of the light.”

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As creatures of the night, bats are often symbols of darkness and sometimes evil. In Western literature, they are often associated with witchcraft. In Shakespeare's Macbeth, written 800 years ago, the witches brew a potion with "Eye of newt and toe of frog, Wool of bat and tongue of dog."

Fortunately, many examples in modern literature, like the children’s book Stellaluna, portray bats in a positive light. With so many available, treat a child in your life to a great bat book!

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Happy Earth Day! The theme for Earth Day 2013 is The Face of Climate Change. Over the next few days, bat facts will focus on climate change impacts on Indiana bats.

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For the little brown bat, climate change models indicate warming will push its winter range north during the next 80 years. A similar shift for the Indiana bat could reduce the bats’ access to the large, complex cave systems it needs for hibernation. Such caves are rare north of the bats’ current range.

Today is Arbor Day, a day to celebrate trees. The tree that you plant today could be the future home of an Indiana bat colony!

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Spring weather can be unpredictable and highly variable. Cold spring weather can affect embryo development in bats and delay birth of pups. Cold weather may even result in some females not having pups.

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Indiana bats emerge from hibernation in April, but where do they go? Adult females head to their maternity colonies. Female Indiana bats are very loyal to their maternity range. They return to the same maternity colony every spring.

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How far do Indiana bats migrate? The longest recorded Indiana bat migration was a female, banded at her maternity colony in Michigan. She migrated 357 miles to a cave in Mammoth Cave National Park in Kentucky.

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While migrations over 300 miles long have been documented, most Indiana bats migrate shorter distances. Twenty-seven Indiana bats banded in Indiana migrated an average of 52 miles, and a study in New York found that bats migrated less than 42 miles.